Differential encoding techniques are used by some communications systems to mitigate the undesirable effects of phase noise and channel impairments. Examples include but are not limited to Quadrature Phase Shift Keying (QPSK), Differentially Encoded QPSK (DE-QPSK), 16 Quadrature Amplitude Modulation (QAM) and 64 QAM QPSK is a form of phase shift keying in which two bits are contemporaneously modulated by selecting one of four possible carrier phase shifts (0, π/2, π, and 3π/2). QAM is a modulation technique for conveying either two analog message signals or two digital bit streams by changing the amplitudes of two carrier waves using Amplitude Shift Keying (ASK) or Amplitude Modulation (AM). When these techniques are used, a differential decoding operation is implemented at the receiver to recover the transmitted information. In particular, a “soft decision” decoder uses soft bit metric information to decode data that has been encoded with an error correcting code. The soft bit metric information indicates the reliability of each input data point, and is used to generate a better estimate of the original data than a hard decision decoder would when the data is corrupted by noise. However, soft bit metric information may be computational costly to generate.